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21 April 2014
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You are here: BBC Science > Human Body & Mind > The Body > Puberty

Boobs and bras

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Boobs are a subject of mystery and concern at puberty, both for boys and girls. What are they like? How big should they be?

Once the ovaries start sending oestrogen around the body, a girl's breasts will begin to grow. This process is gradual, taking as much as four years for full development.

The first sign of growth is when the nipples start to stick out from the chest. Behind the nipple, milk ducts begin to grow. Next, the flat circular part of the nipple, the areola, rises and starts to expand. Glands that make sweat and scent develop beneath it.

The breast begins to fill out, as fat is deposited around the nipple. Initially the breasts stick out in a conical shape. As growth continues they gradually round off into an adult shape.

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The duct system responsible for breast milk starts developing during puberty. Some secretory glands are formed, but the breast will not be capable of producing milk until pregnancy.

 
Many boys will start to develop breasts in their teenage years

Many girls notice swelling and tenderness in the breasts just before their period. This is due to the action of female hormones that increase the amount of water retained in the tissues. As the breasts become larger, a bra will need to be worn for support. Bras are a status symbol among some teenage girls and they will often want to wear one before it is necessary.

Male breasts

Many boys will start to develop breasts in their teenage years. This can be quite alarming for them, but it is perfectly normal and the breast tissue will disappear later on. Breast growth in boys - usually around the ages of 12-14 - is caused by a lag in the production of testosterone. Background levels of female hormones may cause the breast to grow.

As soon as testosterone levels increase, they will swamp the female hormone and the breast growth will disappear. Up to a third of boys experience some breast development on one or both sides. This causes great worry and embarrassment for the affected boy.

Testosterone surges also prepare boys for fatherhood, as they start to get erections.


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